In general, there exist several methods for presenting an image in a PC-compatible format. These include a normal or high band method according to the national television system committee (hereinafter, referred to as NTSC), a normal or high band phase alternation line (hereinafter, referred to as PAL) method, the rule 601 method of international radio consultative committee (CCIR), and the VGA method.
The above methods are different from each other in their image processes. For example, the NTSC and PAL methods are compared and contrasted in the following table.
TABLE I Method Characteristics NTSC PAL the number of scans (H) 525 625 the horizontal 15.734 15.625 frequency (KHz) the vertical frequency 59.94 50 (Hz) picture for every 29.97 25 second (sheet) image band (MHz) 4.2 5 audio carrier (MHz) 4.5 5.5 channel band (MHz) 6 7 chrominance sub carrier 3.579545 4.433618 (MHz)
As mentioned above, even though the plurality of image display methods are each different in broadcasting size, they can be called the PC format in view of a fact that a corresponding image can be displayed on a monitor of a PC. The MPEG technique can make any of the plurality of image processing methods applicable to the current PC.
A conventional image signal is different than an image signal compatible with the MPEG technique. Therefore, it is necessary to generate a synchronization signal adjustable to a given image processing method and there is also required a timing generator for regulating timing.
The timing generator should produce about ten clock signals, in terms of horizontal synchronization, in order to access data of the CCD, i.e., to obtain data from the CCD.
To make such a pulse, there should be designated a rising edge part and a falling edge part in each pulse. The designation operation uses about 20 reference pulses.
FIG. 1 is a diagram illustrating a conventional pulse generator 6. Referring to FIG. 1, there are provided pulse production circuitry 8, a pulse generating circuit 10, a down counter 12, a first NOR gate NOR1, and a second NOR gate NOR2.
In FIG. 1, the pulse generating circuit 10 inputs or receives twenty reference pulse signals P1-P20 from the pulse production circuity 8, a first discriminating signal NTPAL for discriminating the NTSC method from the PAL method, and a second discriminating signal NORHI for discriminating a normal band mode or a high band mode. It compounds the signals according to each state of the discriminating signals to thereby output five mode decision pulse signals DD1-DD5.
The down counter 12 of FIG. 1 inputs or receives the mode decision pulse signals DD1-DD5 from the pulse generating circuit 10, and down-counts the signals by a control signal from the second NOR gate NOR2 (to be discussed further below). The first NOR gate NOR1 inputs or receives signals from nodes within the down counter 12 and outputs a logical NOR combination of these signals as the signal MSC. The second NOR gate NOR2 inputs or receives the MSC signal and a horizontal synchronization detection signal HD and outputs a logical NOR combination of these signals to the down counter 12 as a control signal thereof.
The pulse generating circuit 10 according to the conventional art combines the reference pulse signals P1-P20 differently according to the normal or high band mode of the NTSC method or the normal or high band mode of the
method, i.e., according to the different logic states of the first and second discriminating signals NTPAL and NORHI. The conventional art has pulse production circuits 8 and pulse generating circuits 10 corresponding to each of the four modes, respectively.
The pulse generator 6 according to the conventional art is intended to mux and set the reference pulse signals. The output signal MSC from the first NOR gate NOR1 is provided to the second NOR gate NOR2 through a feed-back connection.
The mode decision pulse signals DD-DD5 are inputted to the down counter 12. The down counter 12 subtracts a counting value from loading values by 1 every clock pulse, and finally outputs a counting value "0". Here, if data outputted from the down counter 12 are all "0", the output signal of the first NOR gate is at the high state.
The pulse generator according to the conventional art is applied to only the normal or high band mode of the NTSC method, or the normal or high band mode of the PAL method. The number of pulses supplied as the reference pulse signals is fixed as 20, i.e., P1-P20. Thus, in case that the size of the CCD, or the number of the pixels of the CCD is changed, and in case that a new method should be applied to the pulse generator, there arises a problem in that it is difficult to apply the new method to the pulse generator according to the conventional art.